The most efficient metazoan swimmer creates a ‘virtual wall’ to enhance performance

It has been well documented that animals (and machines) swimming or flying near a solid boundary get a boost in performance. This ground effect is often modeled as an interaction between a mirrored pair of vortices represented by a true vortex and an opposite sign ‘virtual vortex’ on the other side of the wall. However, most animals do not swim near solid surfaces and thus near body vortex-vortex interactions in open-water swimmers have been poorly investigated. In this study we examine the most energetically efficient metazoan swimmer known to date, the jellyfish Aurelia aurita, to elucidate the role that vortex interactions can play in animals that swim away from solid boundaries. We used high speed video tracking, laser-based digital particle image velocimetry (dPIV) and an algorithm for extracting pressure fields from flow velocity vectors to quantify swimming performance and the effect of near body vortex-vortex interactions. Here we show that a vortex ring (stopping vortex), creat...

已有充分文献记载，动物（及机器）在固体边界附近游泳或飞行时性能会得到提升。这种地面效应（Ground effect）常被建模为一对镜像涡之间的相互作用——由真实涡与壁面另一侧符号相反的“虚拟涡”构成。然而，大多数动物并不在固体表面附近游泳，因此开阔水域游泳者的近体涡-涡相互作用研究尚不充分。本研究以迄今为止已知能量效率最高的后生动物（Metazoan）游泳者——水母Aurelia aurita为对象，阐明涡相互作用在远离固体边界游泳的动物中所扮演的角色。我们采用高速视频跟踪、基于激光的数字粒子图像测速（digital particle image velocimetry，dPIV）以及一种从流速矢量提取压力场的算法，来量化游泳性能及近体涡-涡相互作用的影响。在此，我们发现一个涡环（停滞涡，Stopping vortex）...